What is canker?
Canker is now rarely seen but is a serious infection of the horn of the foot, which results in the formation of a soft, moist, disintegrating growth of horn. It most commonly affects the hind feet and is most often seen in horses kept in wet tropical climates, or in large draught type horses. It is predisposed by long heel conformation which results in deep sweaty sulci (clefts) adjacent to the frog.
What causes canker?
Infection is most commonly associated with bacterial and sometimes fungal invasion of the epidermal horn of the foot, starting around the frog and extending to the sole and wall. In advanced cases infection may enter the underlying sensitive laminae of the hoof.
How is canker diagnosed?
In the early stages, a foul-smelling, moist, vegetative mass of horn is seen, although lameness is rarely encountered. The characteristic, fragile, fronds of horn growth start at the back of the frog and are sometimes covered with a crusty overgrowth. In advanced cases, a cauliflower-like proliferative growth may be seen along the heels, bars, sole and hoof wall and lameness may develop at this stage. Affected horses may stamp the affected foot, reflecting irritation. If deeper tissues are involved, there may be swelling of the pastern and lower limb. Radiographic (x-ray) examinations may be required to determine the extent of the damage to the bony structures of the foot and the collateral cartilages (sidebones).
How is canker treated?
Your veterinary surgeon will thoroughly clean the sole, sulci and frog, debriding and curetting (removing) all abnormal, dead and infected tissues, under general anaesthesia, if necessary. The clean wound is then packed with sterile gauze soaked in antiseptic solution (e.g. dilute povidone iodine) and the foot is bandaged. The horse will often require treatment with antibiotics, active against both aerobic and anaerobic bacterial infections and so the cleaned area may first be swabbed, to determine which bacteria or fungi are present, in order to determine the most appropriate antibiotic or antifungal treatment to use. Tetanus antitoxin must be given, if the horse is not fully vaccinated up to date or if vaccination status cannot be confirmed.
Afterwards, you must ensure clean, dry stable conditions and the bandage and antiseptic gauze pack must be changed every 2-3 days until there is no more discharge and the tissues appear healthy and healing. The horse must be kept out of wet and muddy conditions until the wound is completely healed. When recovered, the affected foot should be re-shod and any hoof malformation should be gradually corrected.
How can canker be prevented?
Prevention is always better than cure and canker can be avoided by good stable management, and regular foot care and inspection. You should stable your horse in clean dry conditions and you should exercise your horse regularly. Your horses’ feet should be regularly trimmed and shod, in order to avoid the development of long heel conformation and to keep the frog healthy.
The prognosis for complete recovery for true canker is always more guarded than for thrush. The prognosis for complete resolution is poor for long-standing cases with spread to the sole involving deeper tissues, because recurrence is common, especially in those horses with hoof deformity.
Make sure that your horses are always fully vaccinated against tetanus, an invariably fatal infection which can gain access through hoof injuries.